Copolyester of cyclohexanedimethanol and process for producing such polyester

ABSTRACT

Disclosed is a process for producing copolyesters having repeat units from a dicarboxylic acid component comprising at least 90 mol % terephthalic acid and a glycol component comprising about 10-95 mol % 1,4-cyclohexanedimethanol and from about 90-5 mol % ethylene glycol comprising reacting the dicarboxylic acid component and the glycol component at temperatures sufficient to effect esterification or transesterification and polycondensing the reaction product in the presence of a catalyst and inhibitor system consisting essentially of Mn, Zn, Ti, Ge and P, all parts by weight based on the weight of the copolyester.

TECHNICAL FIELD

The present invention relates to copolyesters of1,4-cyclohexanedimethanol (CHDM) and a process for producing suchcopolyesters by esterification (or ester interchange) followed bypolycondensation under vacuum for about 2 hours to about 5 hours in thepresence of a selected catalyst and inhibitor system. The product isessentially colorless, clear, and is especially useful in the productionof sheet material of about 1/16 to 1 inch (1.6 mm to 25.4 mm) inthickness.

BACKGROUND OF THE INVENTION

High quality CHDM modified poly(ethylene terephthalate) (PET) isdifficult to manufacture. This is particularly true for those PET'smodified with higher levels of CHDM, e.g. greater than 10 mol % CHDM.The choice of catalyst metals is essential to properly manufacture thesecopolymers with regard to particular properties, such as yellowness andclarity. Titanium catalysts tend to yield copolymers with a yellowcoloration. Antimony and cobalt catalysts tend to be reduced to themetal, thus giving a grayish appearance to the copolymers and greatlyreduces clarity. Good quality copolymers can only be prepared with theproper choice of catalysts, and the choices are not obvious due tointeraction of a certain combination of catalysts.

It has been found that the choice of the proper catalyst system isdependent on the reaction process used. The choice of catalysts as afunction of reactor residence time is not obvious because of theresponse of copolymer properties to the residence time and catalystlevels. Processes with relatively short residence time (shorter thanabout 2 hours) in the polycondensation reactor calls for an activecatalyst system so that the molecular weights can build up quickly inthe relatively short time available. Active catalysts such as titaniumor gallium yield copolymers with the required rate of molecular weightincrease. However, the rates of the side reactions are also fast, sothat the resulting copolymer is unacceptably yellow. Stabilization withphosphorus yields good color copolymers but the reaction rate becomesunacceptably slow. Toning with blue toners such as cobalt reduces theclarity of the copolymers.

According to the present invention, a carefully chosen combination ofcatalysts provides these copolymers with low color and high clarity forreactions with relatively long residence times in the polycondensationreactor.

While all of the catalyst metals have been disclosed for the preparationof polyesters, we are unable to find any prior art that takes advantageof a combination of catalysts with the interactions as we havediscovered. Furthermore, we have found no mention in the literature onthe important effect of polycondensation time on the choice of catalystsystems and the properties of the copolymers.

DESCRIPTION OF THE INVENTION

According to the present invention there is provided a process forproducing copolyesters having a dicarboxylic acid component and a glycolcomponent, the dicarboxylic acid component comprising repeat units fromat least 90 mol % terephthalic acid and the glycol component comprisingrepeat units from about 10-95 mol % 1,4-cyclohexanedimethanol and fromabout 90-5 mol % ethylene glycol, the process comprising reacting thedicarboxylic acid component and the glycol component at temperaturessufficient to effect esterification or ester exchange and polycondensingthe reaction product under an absolute pressure of less than 10 mm Hgfor a time of more than about 2 hours in the presence of a catalyst andinhibitor system consisting essentially of about 0-75 ppm Mn, about25-100 ppm Zn, about 0.5-15 ppm Ti, about 5-80 ppm P, and 0 to about 60ppm Co all parts by weight based on the weight of the copolyester.

Also, the present invention provides copolyesters produced by theprocess described above, and a catalyst and inhibitor system for use inthe process.

Either dimethyl terephthalate (or other lower dialkyl terephthalateester) or terephthalic acid can be used in producing the copolyester.These materials are commercially available.

The glycols used in the copolyester according to the present inventionare CHDM and ethylene glycol. Both of these glycols are commerciallyavailable.

The copolyesters used in making the articles of this invention have 100mol % of a dicarboxylic acid portion and 100 mol % of a glycol portion.The dicarboxylic acid portion of the copolyesters comprises repeat unitsfrom at least 90 mol % terephthalic acid. Up to about 10 mol % of thedicarboxylic acid repeat units may be from other conventional acids suchas those selected from succinic, glutaric, adipic, azelaic, sebacic,fumaric, maleic, itaconic, 1,4-cyclohexanedicarboxylic, phthalic,isophthalic, and naphthalene dicarboxylic acid.

The glycol component of the copolyesters contains repeat units fromabout 10-95 mol % 1,4-cyclohexanedimethanol and about 90-5 mol %ethylene glycol. The glycol component may include up to about 10 mol %of conventional glycols such as propylene glycol, 1,3-propanediol;2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-l,3-propanediol,2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol,1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol,1,6-hexanediol, 1,8-octanediol, 2,2,4-trimethyl-1,6-hexanediol,thiodiethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol and the like.

Branching agents such as, but not limited to, trimellitic acid,trimellitic anhydride, pentaerythritol, may be added for desiredproperties.

Generally, the copolyesters may be produced using conventionalpolyesterification procedures described, for example, in U.S. Pat. Nos.3,305,604 and 2,901,460, the disclosures of which are incorporatedherein by reference. Of course, esters of the acids (e.g., dimethylterephthalate) may be used in producing the polyesters.

Either the cis or trans isomer of CHDM, or mixture thereof, may be usedin accordance with the present invention.

In producing the copolyester according to this invention, a reaction mixof the dicarboxylic acids (or esters as described herein) and glycols isprepared. Mn and/or Zn and Ti are added at the beginning of the process(ester exchange reaction). P and Co (if used) are added after esterexchange. The catalysts and inhibitors can be mixed or added separately.Preferably, P is added after Co.

In the preparation of polyesters by means of the ester interchangereaction, the process comprises two steps. In the first step, glycol anddiester such as dimethyl terephthalate are reacted at elevatedtemperatures. Thereafter, the reaction product is heated under stillhigher temperatures and under reduced pressure to form polyester withthe elimination of glycol, which is readily volatilized under theseconditions and removed from the system. The second step, orpolycondensation step, is continued under higher vacuum until a polymerhaving the desired degree of polymerization, determined by inherentviscosity, is obtained. Without the aid of a suitable catalyst, theabove reactions do not proceed at a noticeable rate.

In the preparation of polyester by direct esterification, polyesters areproduced by reacting a free dicarboxylic acid with a glycol at apressure of from about 1 to about 1000 pounds per square inch gaugepressure to produce a low molecular weight linear or branched polyesterproduct having an average degree of polymerization of from about 1.4 toabout 10. This low molecular weight polymer can then be polymerized bypolycondensation reaction.

The present process can be advantageously operated as a continuousprocess. High molecular weight linear or branched polyesters can beproduced continuously by continuously adding free dicarboxylic acid andglycol to molten low molecular weight linear or branched polyester resinand reacting them while continuously withdrawing low molecular weightresin and introducing the resin withdrawn into a polymerizationapparatus and continuously polymerizing it to high molecular weightresin and withdrawing high molecular weight linear or branched polyesterresin from the polymerization apparatus.

If used, manganese is preferably used as a salt. Examples of suitablemanganese salts are manganous benzoate tetrahydrate, manganese oxide,manganese acetate, manganese acetylacetonate, manganese succinate,manganese glycolate, manganese naphthanate and manganese salicylsalicylate.

The zinc portion of the catalyst system is preferably added as a salt.Examples of suitable salts include zinc acetate, zinc citrate, zinclactate, zinc nitrate, zinc glycolate, etc.

The titanium is preferably added as titanium tetraalkoxide, e.g,titanium tetraisopropoxide, titanium tetraethoxide or titaniumtetrabutoxide.

The phosphorus is preferably added as trialkyl phosphate, triphenylphosphate, or phosphoric acid.

The blue toner is preferably cobalt, and is preferably added as a salt.

Examples of suitable cobalt salts are cobaltous acetate tetrahydrate,cobaltous nitrate, cobaltous chloride, cobalt acetylacetonate, cobaltnaphthanate and cobalt salicyl salicylate.

The levels of the catalysts and inhibitors used with dimethylterephthalate based copolymers are as follows:

Mn, from 0 to 75 ppm, preferably from 20 to 50 ppm, (catalyst)

Zn, from 25 to 100 ppm, preferably from 50 to 80 ppm, (catalyst)

Ti, from 0.5 to 15 ppm, preferably from 1 to 6 ppm (catalyst)

P, from 5 to 80 ppm, (inhibitor), preferably 10 to 30 ppm

Other mild catalysts, such as Ge, can be added but are not necessary.

Co from 0 to 60 ppm or an organic blue toning agent at the proper levelto control the color.

The levels of the catalysts for terephthalic acid based copolymers areas follows:

Zn, from 25 to 100 ppm, preferably from 50 to 80 ppm, (catalyst)

Ti from 0.5-15 ppm, preferably from 1 to 6 ppm

P, from 5 to 80 ppm, (inhibitor), preferably from 10 to 30 ppm

Co from 0 to 60 ppm or an organic blue toning agent at the proper levelto control the color. Other mild catalysts, such as germanium, can beadded but are not necessary.

The following examples are submitted for a better understanding of theinvention:

EXAMPLE 1

Preparation of Poly (co-70-ethylene-30-1,4-cyclohexanedimethyleneterephthalate). A 500 mL round-bottom glass flask, equipped with anitrogen inlet, a condensate outlet, an additive inlet and a stirrer, ischarged with 0.5 mol of dimethyl terephthalate, 0.845 mol of ethyleneglycol, 0.155 mol of 1,4-cyclohexanedimethanol (CHDM), 25 ppm of Mn asmanganese diacetate, 60 ppm of Zn as zinc acetate, and 2 ppm of Ti astitanium isopropoxide. The reaction flask is well purged with nitrogenand immersed into a metal bath preheated to 190° C. The molten mixtureis kept at 190° C. for 60 minutes and the temperature is increased to220° C. After 60 minutes, 14 ppm P as triethyl phosphate and 28 ppm ofcobalt as cobaltous acetate were added and the temperature is increasedto 280° C. After 25 minutes, vacuum is applied and the pressure reducedto 0.1 mm mercury over the course of 210 minutes. The vacuum is relievedto atmospheric pressure using nitrogen. An essentially colorless(b=0.01) compared with b=8.83 for a conventional catalyst system usinghigher (50 ppm Ti levels and no zinc) and clear polymer melt results.The resulting polymer is separated from the flask and ground to pass a 3mm mesh screen.

EXAMPLE 2

Same as Example 1 except amount of CHDM is 0.06 mol, ethylene glycol is1.0 mol and dimethyl terephthalate is 0.5 mol. Color analysis and I.V.are similar to Example 1.

Example 3

Same as Example 1 except amount of CHDM is 0.47 mol, ethylene glycol is0.12 mol and dimethyl terephthalate is 0.5 mol. Color analysis and I.V.are similar to Example 1.

EXAMPLES 4 THROUGH 9

Example 1 is repeated, using the following levels of catalysts,inhibitor and toner:

    ______________________________________                                                                                       Reflec-                                                          Color        tance                          Ex   Ti     Mn     Zn   P    Co   (b)    Clarity                                                                             (Rd)                           ______________________________________                                        4    2      25     40   12   28   -0.11  Good  77.79                          5    8      10     45   26   10   2.95   Good  81.85                          6    6       0     60   20   50   -0.26  Good  75.47                          7    4      30     30   11   15   3.72   Good  79.83                          8    1       0     100  10   30   2.51   Good  78.69                          9    7      75     25   39   10   1.53   Good  83.76                          ______________________________________                                    

The clarity indicated above is that of the copolyester extruded into asheet 3.2 mm in thickness. The color is from the pellets.

Catalyst metals, phosphorus and cobalt are given herein as ppm (partsper million) of the element (not the compound) based on the weight ofpolymer. Calculations are conventional and well known by those skilledin the art. Thus, 98 ppm Ti for a 0.60 mole scale preparation of PETmodified with 30 mol % of 1,4-cyclohexanedimethanol is determined as:##EQU1## The weight of other catalyst metals or other additives iscalculated similarly.

Depending upon the polymer production rate, the catalyst mix feed ratemay be varied to provide the desired catalyst level within the rangespecified by any specific metal, as for 0.5-15 ppm Ti, for instance.Likewise, depending upon the required catalyst mix feed rate, theconcentrations of various components may be adjusted to provide thedesired metal to metal ratios in the range of ratios in parts by weightset forth in this specification.

As mentioned previously, the copolyester according to this invention areespecially useful as materials for producing thick (1.6 to 25.4 mm)sheets. The sheet material may be produced using extrusion or castingtechniques well known in the art.

Whenever the term "inherent viscosity" (I.V.) is used in thisapplication, it will be understood to refer to viscosity determinationsmade at 25° C. using 0.5 gram of polymer per 100 ml of a solventcomposed of 60 wt % phenol and 40 wt % tetrachloroethane.

The color of the polymer is determined using a Gardner XL-23 TristimulusColorimeter manufactured by Gardner Laboratory, Inc., Bethesda, Md.

Unless otherwise specified, all parts, percentages, ratios, etc., are byweight. The designation "ppm" indicates parts per million by weight.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. Process for producing copolyester having repeat units froma dicarboxylic acid component comprising repeat units from at least 90mol % terephthalic acid and a glycol component comprising repeat unitsfrom about 10-95 mol % 1,4-cyclohexanedimethanol and from about 90-5 mol% ethylene glycol comprising reacting said dicarboxylic acid componentand said glycol component at temperatures sufficient to effectesterification or trans-esterification and polycondensing said reactionproduct under absolute pressure of less than 10 mm Hg for a time of morethan about 2 to about 5 hours in the presence of a catalyst andinhibitor system consisting essentially of about 0-75 ppm Mn, about25-100 ppm Zn, about 0.5-15 ppm Ti, about 5-80 ppm P, and 0 to about 60ppm of an organic blue toning agent, all parts by weight based on theweight of the copolyester.
 2. Process for producing copolyesteraccording to claim 1 wherein said dicarboxylic acid component comprisesdimethyl terephthalate.
 3. Process for producing copolyester accordingto claim 1 wherein said dicarboxylic acid component comprisesterephthalic acid.
 4. Process according to claim 1 wherein a blue toningagent is added to said catalyst system.
 5. Process according to claim 4wherein said blue toning agent is cobalt.
 6. Copolyester producedaccording to the process of claim
 1. 7. An extruded sheet having athickness of about 1.6 mm to about 25.4 mm comprising a copolyesterproduced by the process of claim 1.